As a steering control device for automobiles, an electric power steering device is used. The electric power steering device controls a current of an electric motor and transmits an electric motor torque generated according to the current to a steering shaft, thereby reducing a steering torque to be applied by a driver.
In general, the torque generated by the electric motor contains a cogging torque or a torque ripple. The cogging torque and the torque ripple act as disturbance torques to pulsate the steering torque, and hence the steering feel is degraded in some cases. In order to prevent the degradation of the steering feel, an expensive motor has been used so as to reduce the cogging torque and the torque ripple of the motor.
In a conventional steering control device for automobiles, compensation control using the electric motor is performed so as to extract a pulsating component due to the cogging torque or the torque ripple to reduce the pulsation of the steering torque (for example, see Patent Document 1).
As another conventional steering control device for automobiles, there is an electric power steering device using a variable time-constant filter. In the electric power steering device, noise is removed by a lowpass filter having a time constant that is variable according to an angular velocity of a steering wheel (for example, see Patent Document 2).
Patent Document 1: JP 2005-67359 A (FIG. 1)
Patent Document 2: JP 3884236 B (FIG. 3)